Compressor structure



Jan. 23, 1968 J. c. BURGE ETAL 3,365,124

COMPRES SOR STRUCTURE Filed Feb. 2l. 1966 MFL@ irme/ffy* United States Patent Office 3,365,124 Patented Jan. 23, lg68 3,365,124 CMPRESSGR STRUCTURE Joseph C. Burge and .lohn D. Naherhaus, Cincinnati,

Ghia, assignors to General Electric Company, a corporation of New York Filed Feb. 21, 1966, Ser. No. 528,860 7 Claims. (Cl. 230-122) ABSTRACT F THE DlSCLOSURE An axial flow compressor includes a row of stator vanes having openings for the extraction of bleed air at their inner tips such that clean air in the inner portion of the flow passageway is extracted.

The present invention relates to compressor structure and, more particularly, to interstage bleed means as applied to a multi-stage axial flow compressor.

In many aircraft applications of gas turbine powerplants employing multi-stage axial flow compressors, there is a requirement for a supply of pressurized air for aircraft use such as cabin pressurization, air conditioning, and anti-icing purposes as Well as other uses. This has led to the supply of air generally from the engine compressor since it is a source of air under many different pressures. By tapping off at any point in a multi-stage axial tiow compressor, substantially any desirable pressurized air supply is available. Of course, the removal of air from the cycle imposes a penalty on engine performance but this is required if the compressor is to be used as a source of air. Additionally, in compressor bleed arrangements it is desirable to maintain close blade-casing clearances to avoid disturbing aerodynamic effects. Many systems have been devised to remove air from the region of the outer end of the rotating blades through the stator casing wall at the O D. of the rotor. Because of the compressors centrifugal effect such air includes entrapped dirt, oil and foreign particles so that air usually requires filtering before use. Systems have also been disclosed to remove air from the I.D. of the compressor since such air is relatively clean air. These LD. systems have generally employed blade or vane tip shrouding in order to avoid recirculating ows or to strengthen members which have been slotted for the removal of the air.

The main object of the present invention is to provide an interstage bleed structure which operates at the rotor LD. with minimum aerodynamic disturbance.

Another object is to provide a system which removes clean air with minimum unequal circumferential, axial, or radial pressure distribution in a compressor.

A further object is to provide a system wherein the losses due to the presence of the removal structure are minimized while obtaining the maximum area for air removal.

A further object is to provide such a system which employs no stator vane tip shrouding and all of the structure for the removal of the air is contained in the vane itself.

Briefly stated, the invention is for use in a multi-stage axial ow compressor which includes a rotor hub having airfoil blades or vanes extending radially therefrom and a casing with plural stages of stator airfoil vanes between the rotor blades whereby the casing and hub define a iiow passage in the conventional manner. At least one of the stator vane stages and the vane platforms are hollow. In this structure an interstage bleed means is provided comprising an elongated slot in at least some of the vanes of the hollow stage. Preferably, the slot is provided in all of the vanes of the stage. The slot is cut back from the tip of the pressure surface and it extends parallel to the hub surface to scoop or scrape the air at the hub into the vane through its concave or high pressure side. The air iiows through the supported hollow vane and through the hollow shank or platform into a collecting manifold that is provided on the outside of the casing bridging the hollow portion of the vanes. The collecting manifold receives the air and directs it to a point of use. Preferably, the slots are rectangular and disposed between the airfoil leading and trailing edges and set back from each edge. The slot is preferably maintained at a minimum height-about equal to the set-back-and the c-ross sectional area of the slot is at least equal to the minimum airfoil cross sectional area for maximum effectiveness.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed the invention will be better understood from the following description taken in connection with the accompanying drawing, in which:

FIGURE l is a partial cross sectional View of a typical interstage bleed means of the present invention;

FIGURE 2 is a partial perspective showing the slot adjacent the hub; and

FIGURE 3 is an enlarged cross section on the line 3 3 of FIGURE l.

Referring first to FIGURE l, there is shown the central portion of a multi-stage axial iiow compressor that includes a rotor drum or hub 10 having rotating airfoil blades 12 thereon in the conventional fashion. A stator casing 14 is provided with the usual inwardly directed radial stator airfoil vanes 16 intermeshed between the rotating blades for raising the pressure of the air passing through fiow passage 18 defined by the casing 14 and hub surface 20 of rotor It).

It is desired to remove pressurized air from some intermediate stage of this multi-stage axial flow compressor for use. The removal means must be such as to minimize amy distortion or pressure unbalance of the airflow through the compressor. Additionally, it is desired to do this with a minimum amount of structure and to avoid vane tip shrouding if possible.

To this end, at least some of the stator vanes 16 and preferably a complete stage of vanes 16 are hollow to provide an internal passage 22 extending through the vane airfoil and shank portion 24 outside of the casing. To avoid aerodynamic disturbance as much as possible and to provide clean air, provision is made for removal of interstage air from the hub surface 20 or at the inner diameter (LD.) of the rotating structure. The structure for doing this consists of an opening, preferably in the form of a rectangular slot 26, that is formed in the high pressure or concave surface 28 as seen in FIGURES 2 and 3. Aerodynamically, this is the non-critical surface of the airfoil as opposed to the low pressure or suction surface 30 on the opposite convex side. Further reducing the aerodynamic effects, the slot is preferably cut back from the tip of the pressure surface as shown and is disposed to extend parallel to the hub surface 20, to, in effect, scrape or scoop off a supply of pressurized air. By having only the preferred side cut back as a slot 26, the scooped air under pressure then flows radially outward through the vane and shank portion 24 to the outer side of the casing 14. In order to collect the air and direct it to a point of use, there is provided a manifold 32 on the casing bridging the hollow platforms or Shanks of the hollow vanes as shown in FIGURE l. The manifold may direct the air in any suitable manner to a distant point of use.

By providing the rectangular slot 26 in the manner shown, it will be apparent that the cross sectional area of the slot must be at least equal to the minimum airfoil cross sectional area if it is not to be a limiting opening.

lf the slot area is greater than the airfoil cross section it will be obvious that it will scoop up more air than can be used because the cross sectional area of the airfol is a limiting dimension. If the slot area is less than the airfoil can handle, then the maximum bleed elfe-ct is not obtained. In order to get the required flow, it will be apparent that the cross sectional area of slot 26 may assume any rectangular shape, It could be tall and narrow and it can be wide and low in height as shown for the same area. It is desired that the slot be low and wide and extend chordwise on the pressure surface as shown to avoid adverse aerodynamic effects that would be present in a siot extending Well into the ilow stream and to obtain the cleanest possible air. The strength of the individual vane must be maintained since it is gen erally constructed of thin sheet metal as shown in FIG URE 3 and so it is supported internally by suitable supporting structure 34 which may also form the passages for the outward removal of air. The strength is maintained by providing the slot in a set-back from the leading and trailing edges as shown at 36 and 38 respectively in FIGURE 1. By maintaining the radial depth of the slot substantially equal to the set-back distance, the most desirable coniiguration for maximum strength, minimum aerodynamic interference, and optimum pressure balance is obtained.

It has been found feasible to minimize the slot openings by providing an entire stage of vanes with such slots. It will be apparent that each slot may then be smaller than if only a few vanes were slotted and the total air removed is a function of the slot area per vane times the number of vanes. This also has the advantage of minimizing any pressure unbalances and disturbances to the ow. Further, slotting an entire stage lreeps the individual vanes smaller and thinner and still permits the removal ofthe maximum amount of air with the minimum aerodynamic disturbance.

Obviously, the slot may be varied depending on the air quantity desired and may take other forms than the rectangular one shown. The manifold 32 may extend over more than the hollow stage in order to obtain the necessary area for handling the removed air and still maintain minimum diameter.

While there has been described a preferred form of the invention, obvious equivalent variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described, and the claims are intended to cover such equivalent variations.

We claim:

1. A multi-stage axial flow compressor including a rotor hub having airfoil blades thereon and a casing having plural stages of and including some hollow stator airfoil vanes between the rotor blades,

said casing and hub defining a flow passage, bleed means comprising,

an air inlet opening means in the pressure surface of a hollow stator vane at the tip thereof adjacent the hub,

said opening means extending in a generally axial direction parallel to the hub surface with its axial extent being substantially greater than its radial extent, and

a collecting manifold on said casing bridging the hollow vane base for receiving said air and directing it to a point of use.

2. Apparatus as described in claim 1 wherein said opening means is a substantially rectangular slot opening in said pressure surface.

3. Apparatus as described in claim 2 wherein said rectangular slot opening extends chordwise on the pressure surface back between the airfoil leading and trailing edges and set back therefrom.

4. Apparatus as described in claim 3 wherein said slot opening radial depth is substantially equal tosaid setback.

5. A multi-stage axial ow compressor including a rotor hub having airfoil blades thereon and a casing having plural stages of stator airfoil vanes between the rotor blades, at least one of said vane stages and platforms therefor being hollow, said casing and hub dening a ilow passage, interstage bleed means comprising,

an elongated slot in each vane of said hollow stage, said elongated slot being cut back from the tip of the pressure surface and extending parallel to the hub surface with its axial extent being substantially greater than its radial extent, and

a collecting manifold around said casing bridging the hollow platforms of said hollow stage for receiving said air and directing it to a point of use.

6. Apparatus as described in claim S wherein said slots are substantially rectangular and extend between the airfoil leading and trailing edges and set back therefrom.

'7. Apparatus as described in claim 6 wherein the radial depth of each slot opening is substantially equal to said set-back and the slot cross sectional area is at least equal to the minimum airfoil cross sectional area.

References Cited UNlTED STATES PATENTS 2,344,835 3/1944 Stalker.

2,656,146 l0/l953 Sollinger 230-132 2,682,363 6/1954 Lombard et al 23d-122 2,720,356 10/1955 Erwin 230-122 2,848,155 8/1958 Hausmann 230-122 2,859,934 1l/l958 Halford et al. 253-39.1l3 2,924,425 2/1960 Cutler 253--39.1

DONLEY I. STOCKING, Primary Examiner.

HENRY F. RADUAZO, Examiner. 

